Locomotion jittering with fixedUpdate and IK

I attached interactive cloth to my character, I use it to simulate hair. It works pretty well without "useIK" enabled in the LegAnimator Script. With IK on, my character starts jittering when fixedUpdate in the characterMotor is enabled at the same time. I think it's some kind of sync problem, I use fixedUpdate in the CharacterMotor, AlignmentTracker, in my PlayerScript even for the Cameramovement, nothing helps. When I use an empty GameObject as root bone in the LegController it stops jittering and at least the IK for the feet works but Accelerate Tilt of couse don't work. I hope somebody has a real solution.